Many processes are known to prepare bisphenols. In some of these processes, a phenol is reacted with a ketone to form the bisphenol. The reaction usually takes place in the presence of an acidic medium including inorganic acids and acidic cation exchange resins. In some cases a mercaptan, such as methyl mercaptan is used as a co-catalyst.
U.S. Pat. No. 2,730,552 describes the preparation of bisphenols in the presence of an inorganic mineral acid and a mercaptan co-catalyst. In such a process where the reactors are traditionally back-mixed, the water concentration is always high throughout the process.
However, in a process, such as described in British Pat. No. 1,185,102, which uses an ion-exchange resin catalyst, the reactor configuration is practically limited to a plug-flow reactor or a series of plug-flow reactors in which the activity of the ion-exchange resin catalyst is adversely affected by water formed in the reaction and therefore activity decreases sharply as the process progresses. Cyclic dimers by-product is a problem in such a process where mercaptan is added to increase the rate of reaction to achieve practical reaction rates when using an ion-exchange resin catalyst.